It is sometimes necessary to expel viscous material from a syringe through a relatively small orifice. One example is in cataract surgery where a viscous material, such as sodium hyaluronate, is injected into the capsular bag to protect regions of the eye as the natural lens is being removed. This viscous material is manually injected utilizing a syringe which is coupled to a cannula which has a relatively small diameter passage extending through it.
One problem with syringes of this type is that it is difficult to generate sufficient force to extrude the viscous material through the small diameter passage of the cannula. One way to solve this problem would be to increase the diameter of the passage in the cannula. However, for applications such as eye surgery, this is not desirable because of the need to use instruments of the smallest possible size in the eye.
Another possible solution would be to utilize a syringe having a smaller cross sectional area bore which could generate a higher pressure on the viscous material. However, the commercially available smaller bore syringes known to either of us do not have a strong connector, such as a Luer lock fitting for coupling the syringe to the cannula or are otherwise not as desirable for the injection of viscous material into the capsular bag. A strong connector is essential because with the relatively high pressures generated, a weak connector may fail in which event the cannula becomes a missile which can shoot into the patient's eye causing injury.